Distribution, characteristics, and some acoustic implications of oceanic fronts in the North Atlantic

Oceanic fronts and eddies occur throughout the North Atlantic, but are most evident in the western and northern regions. The Gulf Stream is the dominant front in the Atlantic and is also the source of both cyclonic and anticyclonic eddies. These features are 100–200 km in diameter and have life-times of 1–2 years; as many as 13 have been observed to exist at one time in the vicinity of the Gulf Stream. Acoustic ray traces and intensities for various receiver depths were calculated across the Gulf Stream using AXBT temperature profiles and historical sound velocity data. When sound intensities across the Gulf Stream were compared to intensities for similar situations without a front, it was found that the Gulf Stream North Wall could significantly increase or decrease propagation loss depending on distance of the receiver from the front; the maximum difference was 18 dB. The South Wall of the Stream had no significant effect on sound intensity. Three-dimensional propagation loss diagrams show that effects of the North Wall on propagation loss are evident at all depths from sea surface to 1000 m. It is clear that oceanic fronts and eddies must be included in any realistic acoustic model.